The present invention relates to a chuck. More particularly this invention concerns a collet chuck for attachment to a mounting collar of a workpiece to be machined or of a tool.
A standard collet chuck for attachment to a mounting collar of a tool or workpiece has a body formed centered on an axis with a forwardly open socket shaped to coaxially receive the mounting collar. A collet inside the body has a plurality of jaws with front ends that project axially forward into the collar. The jaws can rock to move the front ends radially outward to engage behind an axially forwardly directed shoulder of the collar and thereby lock the collar to the chuck body. Each jaw can pivot in the body about a respective axis extending in a plane perpendicular to the axis and offset therefrom. An axially displaceable cam sleeve inside the body has a radially outwardly directed front cam surface engageable with front inside faces of the front ends of the jaws and a radially outwardly directed rear cam surface engageable with rear inside faces of rear ends of the jaws. Thus, when displaced axially rearward, the cam sleeve spreads the front ends of the jaws to hold the workpiece and, when displaced axially forward, rocks these front ends inward to release the workpiece. Such a chuck is described in German patent document 4,138,974 of E. Brangs.
In such a system it is possible for the cam sleeve and the jaws to move into slightly offcenter positions. The chuck will hold the workpiece adequately with the parts offcenter, but will be somewhat eccentrically off balanced. Since it is not uncommon for such a chuck to rotate at very high speed, as much as 40,000 RPM, even a minor imbalance can create a problem, for instance a vibration that ruins the machining job.
It is therefore an object of the present invention to provide an improved collet chuck.
Another object is the provision of such an improved collet chuck which overcomes the above-given disadvantages, that is which maintains its cam sleeve on center at all times.
A collet chuck for holding a mounting collar of an objectxe2x80x94tool or workpiecexe2x80x94to be rotated has according to the invention a chuck body centered on and rotatable about an axis and formed with a forwardly open socket shaped to receive the collar. A plurality of jaws in the socket have front ends engageable inside the collar in the socket and rear ends offset axially rearwardly therefrom. The jaws are angularly spaced and define axially extending and radially inwardly open slots. A setting sleeve has a front cam surface engageable with inner faces of the front ends of the jaws so that the sleeve can cam out the front ends to lock the jaws to the collar in the socket. The sleeve is formed with radially outwardly projecting and axially extending ribs each received in a respective one of the slots.
Thus with this system the ribs keep the sleeve and jaws perfectly in position in the chuck body. The jaws in particular cannot shift angularly, and the sleeve is rotationally locked to the jaws and also centered by them. The result is a perfectly balanced chuck that can be rotated at high speed with no vibration or throw. The ribs can be axially quite long, basically extending axially from the front jaw ends at least to the middle of the jaws.
According to the invention the chuck body is formed axially rearward of the socket with a radially inwardly open groove centered on the axis and each jaw has a rear end received and radially displaceable in the groove. The setting sleeve has a rear cam surface engageable with inner faces of the rear ends of the jaws so that the sleeve can cam out the rear ends to move the front ends radially inward and axially clear of the collar in the socket. Each of the ribs is of an angular dimension increasing outward from the axis so as to stay on center regardless of the positions of the jaws, basically of an inverted Y-shape. Further each of the ribs extends at least from the axial rear edge of the front cam surface to the axial front edge of the rear cam surface to keep all the parts aligned. The ribs are produced by milling after the basic cam sleeve has been made by turning, for a relatively low production cost.
According to the invention a spring engaged around the rear ends of the jaws urges the jaw front ends radially outward. The rear ends form a radially outwardly open groove receiving the spring. This spring has spacer blocks engaged in the slots and braced angularly against the jaws so that the spacer blocks angularly space and separate the jaws. As a result the subassembly formed by the spring and jaws can easily be installed in the chuck body simply by pushing it axially rearward into the socket until the rear ends align with the groove. Subsequent insertion of the sleeve completes the assembly and makes it impossible for the jaws to pull axially out of the chuck body.
The sleeve according to the invention is formed axially rearward of the rear cam surface with a cylindrical holding surface centered on the axis and engageable with the jaw rear ends to retain same in a freeing position with the jaw front ends shifted inward. Thus when the sleeve is shifted all the way forward it first cams out the rear ends with its frustoconical rear cam surface, then holds them in the outer position without having to maintain an axial force on the sleeve. Thus the chuck can be locked in the open position.
The groove has an axially rearwardly directed flank engaging the jaw rear ends. This flank has a radially outer portion lying substantially in a plane perpendicular to the axis and a frustoconical radially inner portion inclined at about 10xc2x0 to the plane. As a result the jaws shift somewhat axially rearward as the rear ends move radially inward, providing a very strong connection.